Convergent gene loss in aquatic plants predicts new components of plant immunity and drought response

Abstract

Plant innate immunity relies on NLR receptors that recognize pathogen derived molecules and activate downstream signalling pathways. We analyzed the variation in copy number of NLR genes across flowering plants, and identified a number of species with a low number of NLRs relative to sister species. Two distinct lineages, one monocot (Lentibulariaceae) and one dicot (Alismatales) encapsulate four species with particularly few NLR genes. In these lineages, loss of NLRs coincided with loss of the well-known downstream immune signalling complex (EDS1-PAD4). When we expanded our analysis across the whole proteomes, we were able to identify other characterized immune genes absent only in Lentibulariaceae and Alismatales. Additionally, we identified a small subset of genes with unknown function convergently lost in all four species. We predicted that some of these genes may have a role in plant immunity. Gene expression analyses confirmed that a group of these genes was differentially expressed under pathogen infection. Another subset of these genes was differentially expressed upon drought providing further evidence of a link between the drought and plant immunity.